The present invention relates to an automatic control apparatus in a printing press, which automatically mounts a printing plate on a plate cylinder and forms an ink film thickness distribution corresponding to the image of the printing plate, as a series of work steps.
FIG. 7 shows the schematic arrangement of an ink supply unit in each printing unit in a web offset printing press. Referring to FIG. 7, reference numeral 1 denotes an ink fountain. An ink 2 is stored in the ink fountain 1. An ink fountain roller 3 supplies the ink stored in the ink fountain 1. A plurality of ink fountain keys 4 are arranged parallel to each other in the axial direction of the ink fountain roller 3. Reference numeral 5 denotes an ink ductor roller; and 6, an ink roller group. The ink ductor roller 5 is arranged between the ink fountain roller 3 and the uppermost-stream roller of the ink roller group 6. A printing plate 7 is mounted on the circumferential surface of a plate cylinder 10. Reference numeral 8 denotes dampening water. A dampening roller group 9 supplies the dampening water 8 to the printing plate 7 mounted on the plate cylinder 10. A blanket cylinder 20 opposes to the plate cylinder 10.
In this ink supply unit, the ink 2 in the ink fountain 1 is supplied to the ink fountain roller 3 by adjusting the aperture pat of the ink fountain keys 4. The ink 2 supplied to the ink fountain roller 3 is supplied, by the ducting operation of the ink ductor roller 5, to the printing plate 7 mounted on the circumferential surface of the plate cylinder 10 through the ink roller group 6. Along with this ink supply operation, the dampening water 8 is supplied to the printing plate 7 through the dampening roller group 9.
When an old printing plate is replaced for a new printing plate 7, the aperture pat of the ink fountain keys 4, the rotation ratio of the ink fountain roller 3, the supply amount of the dampening water 8, and the like are preset in accordance with the image of the printing plate 7. More specifically, the aperture pat of the ink fountain keys 4, the rotation ratio of the ink fountain roller 3, the supply amount of the dampening water 8, and the like are set at values that match the image of the printing plate 7. Then, the ink 2 in the ink fountain 1 is supplied to the printing plate 7 through the ink roller group 6, and the dampening water 8 is supplied to the printing plate 7 through the dampening roller group 9. In this case, test printing is performed before final printing to adjust the ink supply amount, thereby obtaining a satisfactory color tone. Hence, a desired ink film thickness distribution (gradient of the ink film thickness) is formed in the ink roller group 6.
In a conventional ink supply unit, when the old printing plate is replaced for the new printing plate 7, an ink film thickness distribution corresponding to the old printing plate remains in the ink roller group 6. In this case, the ink film thickness distribution for the old printing plate must be gradually changed to that for the new printing plate 7, and ink supply amount adjusting operation and test printing operation must be excessively performed until a satisfactory color tone is obtained.
From the above reason, in order to decrease the number of times of adjustment of the ink supply amount and the number of times of test printing that are to be performed until a satisfactory color tone is obtained, the present applicant proposes "an ink film thickness control method" in U.S. Ser. No. 08/884,349.
According to this ink film thickness control method, in replacing an old printing plate for a new printing plate 7, the ink is removed. More specifically, the ducting operation of the ink ductor roller 5 is turned off, and the printing press is operated while the old printing plate is mounted, to perform printing by a predetermined number sheets. As a result, as shown in FIG. 8A, only a minimum ink film thickness distribution (to be referred to as the basic ink film thickness distribution hereinafter) Ma, which is required during printing, is left in the ink roller group 6 to decrease from the upstream to the downstream.
The blanket cylinder (not shown) is cleaned, the old printing plate is replaced for the new printing plate 7, and pre-inking II is performed. More specifically, the aperture pat of the ink fountain keys 4, the rotation ratio of the ink fountain roller 3, the supply amount of the dampening water 8, and the like are preset in accordance with the image of the new printing plate 7, and the printing press is operated. Hence, the ink ductor roller 5 is caused to perform the ducting operation a predetermined number of times, to superpose, on the basic ink film thickness distribution Ma left in the ink roller group 6, an ink film thickness distribution (to be referred to as the image ink film thickness distribution) Mb in accordance with the image of the new printing plate 7, as shown in FIG. 8B.
While the image ink film thickness distribution Mb is superposed on the basic ink film thickness distribution Ma, test printing is performed by the predetermined number of sheets, and the test-printed matter is subjected to density check. In this density check, if a satisfactory color tone is obtained, ink film thickness control by pre-inking II is ended, and the printing press is shifted to final printing. If no satisfactory color tone is obtained, the image ink film thickness distribution Mb is finely adjusted by pre-inking (+) or pre-inking (-), and test printing is performed again.
Regarding cleaning of the blanket cylinder after ink removing, a cylinder cleaning apparatus described in U.S. Pat. No. 5,515,782 (Reference 1) may be used. Regarding replacement of the printing plate after cleaning the blanket cylinder, a plate replacing apparatus described in U.S. Pat. No. 5,406,888 (Reference 2) may be used. With the cylinder cleaning apparatus of Reference 1, the cleaning web can be urged against the circumferential surface of the blanket cylinder by a single switch operation to clean the blanket cylinder automatically. With the plate replacing apparatus of Reference 2, if the new printing plate 7 is set in the plate replacing apparatus in advance, replacement from the old printing plate to a new printing plate 7 can be performed automatically with a single switch operation.
The work procedure required in this case is as follows. Ink removing is selected on the menu window, to form the basic ink film thickness distribution Ma in the ink roller group 6 by an ink removing operation. The blanket cylinder cleaning unit is actuated by a switch operation to clean the blanket cylinder. Thereafter, the plate replacing apparatus is actuated by a similar switch operation, to replace the old printing plate for the new printing plate 7. Subsequently, pre-inking II is selected on the menu window to perform the operation of pre-inking II.
When the ink roller group 6 does not have an ink, e.g., when the printing plate 7 is to be set on the plate cylinder 10 for the first time, the plate replacing apparatus is actuated by a switch operation to mount the printing plate 7 on the plate cylinder 10. Then, pre-inking I is selected on the menu window to perform the operation of pre-inking I.
In the operation of pre-inking I, the ink fountain keys 4 are set to a predetermined aperture pat (e.g., 50%) and the rotation ratio of the ink fountain roller 3 is set to a predetermined value (e.g., 50%). The printing press is operated to perform the ducting operation of the ink ductor roller 5 a predetermined number of times. The basic ink film thickness distribution Ma (FIG. 7A) is accordingly formed in the ink roller group 6. Thereafter, the aperture pat of the ink fountain keys 4 and the rotation ratio of the ink fountain roller 3 are set to values that match the image of the printing plate 7, and the ducting operation of the ink ductor roller 5 is performed a predetermined number of times. As a result, the image ink film thickness distribution Mb (FIG. 7B) is superposed on the basic ink film thickness distribution Ma formed in the ink roller group 6.
While the image ink film thickness distribution Mb is superposed on the basic ink film thickness distribution Ma, test printing is performed for a predetermined number of sheets, and the test-printed matter is subjected to density check. In this density check, if a satisfactory color tone is obtained, ink film thickness control by pre-inking I is ended, and the printing press is shifted to final printing. If no satisfactory color tone is obtained, the image ink film thickness distribution Mb is finely adjusted by pre-inking (+) or pre-inking (-) and test printing is performed again.
In the conventional method described above, to replace plate, the ink removing operation, the blanket cleaning operation, the plate replacing operation, and the operation of pre-inking II are performed as independent work steps. More specifically, after the ink removing operation is ended, the printing press is shifted to the blanket cleaning operation. After the blanket cleaning operation is ended, the printing press is shifted to the plate replacing operation. After the plate replacing operation is ended, the printing press is shifted to the operation of pre-inking II. The work is repeatedly performed by giving an instruction on the following step in accordance with the operator's judgment while checking the operation state of the previous step. Therefore, a large work load acts on the operator.
When a printing plate is to be mounted on the plate cylinder for the first time, a similar problem arises. More specifically, an instruction for mounting a printing plate on a plate cylinder is sent. After the mounting preparation of the printing plate onto the plate cylinder is ended, an instruction for a shift to the operation of pre-inking I is supplied. In this manner, the operation is performed by giving an instruction on the following step in accordance with the operator's judgment while checking the operation state of the previous step, and accordingly the work load on the operator is also large.